The present invention relates to an impeller for a centrifugal pump.
Impellers for a centrifugal pump typically include at least a carrier body, typically of a carrier disk, and blades arranged thereon. The carrier disk is thereby regularly designed for the rotationally fixed arrangement on a shaft. The impeller blades, depending on the construction type, lie exposed (open impeller) or covered by a shroud, which lies opposite the carrier disk and is connected to the blades. The impellers are known in different construction forms and are applied in single-stage or multistage centrifugal pumps. The impellers typically comprise two or more impeller blades, which may be designed and/or arranged in an equal manner or also in a differing manner.
For example, the impeller represented in FIG. 1 comprises a circular carrier disk 1, which comprises a central recess 2, which is profiled and is envisaged for the rotationally fixed connection to a drive shaft (not shown), as is counted as belonging to the state of the art with centrifugal pumps. A multitude of impeller blades 3 is arranged on the carrier disk 1, which extend at a distance to the recess 2, up to the outer periphery of the carrier disk 1. The blades 3 on the side lying opposite the carrier disk 1 are covered by a shroud 4, which in the embodiment according to FIG. 1 runs out on the inner side into an annular section 5 which forms the run-in of the impeller, as is known per se and is therefore not described in detail.
The shape and the arrangement of the blades 3 may be recognized with a removed shroud 4, as is shown by way of example in FIG. 2. The impeller according to FIG. 2 as a whole comprises six blades 3, which have the same shape and size, and are arranged at the same angular distance on the carrier disk 1.
With impellers formed of plastic, which are manufactured with the injection molding method, as a rule a separate tool is required for each change on the impeller. However, blades of a different arrangement and size may be provided on an impeller, without increasing the manufacturing costs. If, however, the impeller, as is the case with a multitude of centrifugal pumps, is formed of sheet metal, typically of stainless steel sheet metal, then different tools are required for different blade shapes, which increases the manufacturing costs. The manufacture itself is effected by way of aligning the individual blades on the carrier disk and these being welding to this, whereupon, as the case may be, the shroud is applied and likewise welded to the blades.
In order to be able to cover a multitude of application cases, centrifugal pumps are offered in different constructional sizes. The size variation is, however, not only varied by way of changing the geometric dimensions and the drive power, but also by way of variation of the blades. If an impeller, for example, which delivers a certain delivery rate at a given pressure, is to be designed with regard to a reduced delivery rate, then for example the blade height may be reduced accordingly. However, natural limits are placed on this, since a minimum passage height must be retained within the impeller in order to ensure fault-free operation. With cast impellers, it is counted as belonging to the state of the art to fill out intermediate spaces between blade pairs in order to reduce the delivery rate. With impellers manufactured of sheet metal, this is not possible, or only with an increased expense by way of arranging two blades for forming a dead space. However a separate punching tool is necessary for each of these impellers.